The effect of social environment on bird song: listener-specific expression of a sexual signal

Abstract

Animal signals should consistently differ among individuals to convey distinguishable information about the signalers. However, behavioral display signals, such as bird song are also loaded with considerable within-individual variance with mostly unknown function. We hypothesized that the immediate social environment may play a role in mediating such variance component, and investigated in the collared flycatcher (Ficedula albicollis) if the identity and quality of listeners could affect song production in signalers. After presenting territorial males with either a female or male social stimulus, we found in the subsequent song recordings that the among-stimulus effects corresponded to non-zero variance components in several acoustic traits indicating that singing males are able to plastically adjust their songs according to stimulus identity. Male and female stimuli elicited different responses as the identity of the female stimuli affected song complexity only, while the identity of male stimuli altered also song length, maximum frequency, and song rate. The stimulus-specific effect on song in some cases decreased with time, being particularly detectable right after the removal of the stimulus and ceasing later, but this pattern varied across the sex of the stimulus and the song traits. We were able to identify factors that can explain the among-stimulus effects (e.g., size and quality of the stimuli) with roles that also varied among song traits. Our results confirm that the variable social environment can raise considerable variation in song performance, highlighting that within-individual plasticity of bird song can play important roles in sexual signaling.

Individual differences in song plasticity in response to social stimuli and singing position

“…Considering our experimental setup, we can reasonably assume that the changing social environment caused these individually different plastic responses in the song traits over time, possibly because the exposed listener male represented a key stimulus for the focal males. We have previously observed that individuals adjusted the length and MF of their songs to the identity of listener males (Jablonszky et al, 2021). The results found here show that there are also individual differences in the reaction of males to such social challenges.…”

“…Repeatability estimates of song traits revealed that within‐individual variance is considerable even within a short time period (Zsebők et al, 2017). This variance is not stochastic, but may be of biological relevance, as male collared flycatchers seem to alter their song according to the identity of listeners (Jablonszky et al, 2021).…”

“…Three independent song traits with biological relevance in the study population were used during the statistical analysis. Specifically, we considered for each song the song length (SL), maximum frequency (MF), and short‐term complexity (hereafter complexity), which probably play a role in inter‐ or intrasexual communication in the study species (Jablonszky et al, 2021) and has been found to be associated with singing position height (Azar & Bell, 2016; Mathevon et al, 1996; Nemeth et al, 2001). We also extracted the corresponding singing position estimates whenever possible.…”

“…The random part of the model contained year, focal bird identity, a random slope over the order of songs and over the singing positions for focal bird identity with correlations between random intercepts and slopes. The whole random structure for individual identity (intercept, slope for order of songs, slope for singing position) was estimated separately for the three contexts in which the recordings were made, as we expected context-based patterns based on our previous research (Jablonszky et al, 2021). We also considered correlations between random intercepts and slopes across traits (but only within the contexts).…”

“…First, we captured males and females to be used as stimulus birds to elicit songs from the focal males (see details at Jablonszky et al, 2021). Stimulus birds were captured in different study plots (located at least 500 m away) than the tested males.…”